Network Hardware

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Microsoft Powerpoint 2007

PowerPoint is a presentation software package. With PowerPoint, you can easily create slide shows. Trainers and other presenters use slide shows to illustrate their presentations.

Just click here to Learn how to work with power point

Learn More About Viruses

Boot Sector Virus
• Attaches itself to the boot sector of a floppy disk or an executable file
• Copies all or part of itself onto the boot sector of your hard drive when you turn on your computer or try to run an executable file
• Can get one from an infected disk or the Internet

File-Infecting Virus
• Attach themselves to executable files associated with other programs
• Mostly attach to .EXE or .COM files but can infect .SYS, .DLL, and .BIN files
• When you open a program that contains a virus, the virus loads into your computer’s memory and then infects any other executed program.

Macro Virus
• Affect the Microsoft Word and Excel templates
• Once infected, every document or spreadsheet opened with the program becomes corrupted.
• Widespread

Polymorphic Virus
• Can infect the boot sector, files, or both
• Can modify their appearance and signature
• Use code alteration and encryption so that they can not be detected by anti-virus search screens

Stealth Viruses
• Infects a file by adding bytes to the infected file, and then subtracting the same number of bytes to from the directory entry of that file, so that it appears that nothing is different
• Stay in memory

Multipartite Virus
• Can infect the boot sector and executable files
• Combine characteristics of memory-resident and nonresident files, and boot sector viruses incorporating stealth and polymorphic characteristics.

Meta Virus
• The first viruses known to infect data files and work on multiple platforms
• Normally carried in data files for Microsoft Word and AmiPro documents
Other Destructive Programs

Worms
• Often mistaken for a virus
• A single destructive program on a single system
• Often planted by someone with direct access to the system
• Do not replicate themselves

Trojan Horses
• Appears to be a program
• Waits for an user to execute it
• Can infect other files on the system, or other computers on the network

Logic Bombs
• Similar to a Trojan Horse but it has a timing device that is keyed to go off on a certain day or time
• Can do damage anywhere from destroying data on the hard drive to releasing a virus

Computer Viruses

Dear, Sir/Madam

Do you familiar with "Computer Viruses" if not please read below:

A virus is a software program designed to infect, destroy or interfere with a computer or software program. A Virus is a software program capable of reproducing itself and usually capable of causing great harm to files or other programs on the same computer. This computer program can copy itself and infect a computer without the permission or knowledge of the owner. It can be transmitted between computers via networks (especially the Internet) or removable storage such as CDs, USB drives, floppy disks, etc., generally without the knowledge or consent of the recipient. It's a very dangerous computer program with the characteristic feature of being able to generate copies of it (self), and thereby spreading. Additionally most computer viruses have a destructive payload that is activated under certain conditions. A computer virus is a piece of code that is secretly introduced into a system in order to corrupt it or destroy data. Often viruses are hidden in other programs or documents and when opened, the virus is let loose. This is a self-replicating computer program that spreads by inserting copies of itself into other executable code or documents.

A virus can infect other programs by modifying them to include a possibly evolved copy of itself. Programming code created as a prank or as a malicious action that secretly affects other programs and causes unwanted consequences. It can damage system's settings and memory, so it is possible for virus to generate run time error messages as well.

If your computer is already running a virus protection program make sure it has latest updated patch or ".dat" file.


According to my experience a truth is that a true virus cannot spread to another computer without human assistance. So you have to be careful yourself while working at computer/Laptops.

If you are suffering from computer viruses please feel easy to contact me.

What is PSU(Power supply Unit)

PC Power supplies use switcher technology to convert the AC input to lower DC voltages. The 3.3- and 5-volts are typically used by digital circuits, while the 12-volt is used to run motors in disk drives and fans.

If there is any one component that is absolutely vital to the operation of a computer, it is the power supply. Without it, a computer is just an inert box full of plastic and metal. The power supply converts the alternating current (AC) line from your home to the direct current (DC) needed by the personal computer. In this article, we'll learn how PC power supplies work and what the wattage ratings mean.

In a personal computer (PC), the power supply is the metal box usually found in a corner of the case. The power supply is visible from the back of many systems because it contains the power-cord receptacle and the cooling fan.

The term power supply is more commonly abbreviated to PSU, this will be used from hereon in.

Telecommunications equipment is designed to operate on voltages lower than the domestic Mains voltage. In order to reduce this voltage a PSU is used.

To provide a useable low voltage the PSU needs to do a number of things:-

Reduction of AC Mains

This is achieved by using a device known as a Transformer an electromagnetic device consisting of an ferrous iron core which has a large number of turns of wire wound around it, known as the Primary Winding

The ends of these turns of wire being connected to the input voltage (in this case Mains AC).

A second number of turns of wire are wound around the Primary Winding, this set being known as the Secondary Winding.

The difference between the number of turns provides us with a way of reducing (in our case) a high AC voltage to a lower one.

Conversion of AC to DC

To convert our now low AC voltage to DC we use a Rectifier Diode connected to the Secondary Winding.

This is a silicon diode, which has operation analogous to a bicycle tyre valve (as the valve only allows air to flow into the tyre, the diode only allows current to flow in one direction)

As our low AC voltage will be working at a frequency of 50Hz (Mains AC frequency) it is desirable to reduce the inherent hum on this to a lower level.

This is achieved by a technique known as Smoothing (“Ironing” out the bumps in the AC).

A simple way to reduce the hum is to use Full Wave Rectification.

Today this is usually done by four diodes in a bridge configuration known as a Bridge Rectifier. (This can be four individual diodes or a dedicated self contained package)

Regulation of Output Voltage

The Electrolytic Capacitor is a device capable of storing energy the amount of energy and the time it remains stored depending on the value.

In a simple PSU the easiest way to provide regulation to compensate for varying load conditions is to use a pair of relatively high value Electrolytic Capacitors.

Their values in this case being in the region of 470uF to 2000uF depending on the application and the amount of current required from the output of the unit.

One of these capacitors is connected across the DC output of the rectifier diode(s) or bridge, this capacitor also providing an extra degree of smoothing the output waveform.

The second capacitor is connected via a low value, medium to high wattage resistor, which assists in limiting the current demand.

Protection against excessive voltages

In a simple PSU the easiest way to do this is by providing fuses at the input to the transformer, generally in the live side of the mains supply, also at the DC outputs.

In the event of an excessive input voltage, or excessive current being drawn from the output, one of these fuses should normally blow protecting the PSU and the equipment connected to it.

The transformer may also be fitted with an internal or external thermal fuse, which will open if the transformer becomes hot due to the aforementioned conditions.

Other PSU’s

There are lots of other types of PSU, some of which are much more complex in their design and operation and are beyond the scope of this overview.

Power supplies, often referred to as "switching power supplies", use switcher technology to convert the AC input to lower DC voltages. The typical voltages supplied are:

3.3 volts

5 volts

12 volts

The 3.3- and 5-volts are typically used by digital circuits, while the 12-volt is used to run motors in disk drives and fans. The main specification of a power supply is in watts. A watt is the product of the voltage in volts and the current in amperes or amps. If you have been around PCs for many years, you probably remember that the original PCs had large red toggle switches that had a good bit of heft to them. When you turned the PC on or off, you knew you were doing it. These switches actually controlled the flow of 120 volt power to the power supply.

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Today you turn on the power with a little push button, and you turn off the machine with a menu option. These capabilities were added to standard power supplies several years ago. The operating system can send a signal to the power supply to tell it to turn off. The push button sends a 5-volt signal to the power supply to tell it when to turn on. The power supply also has a circuit that supplies 5 volts, called VSB for "standby voltage" even when it is officially "off", so that the button will work.